1. 描述你的问题
   iOS 夜间模式 实现原理

2. 贴上相关代码

-(BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions { self.window = [[UIWindow alloc]initWithFrame:[UIScreen mainScreen].bounds]; self.window.backgroundColor = [UIColor whiteColor]; [self.window makeKeyAndVisible]; ViewController *rootVC = [[ViewController alloc]init]; UINavigationController *nav = [[UINavigationController alloc]initWithRootViewController:rootVC]; UIView *view = [[UIView alloc]init]; view.backgroundColor = [UIColor grayColor]; view.alpha = 0.4; view.userInteractionEnabled = NO; [nav.view addSubview:view]; [view mas_makeConstraints:^(MASConstraintMaker *make) { make.edges.mas_equalTo(nav.view); }]; self.window.rootViewController = nav; return YES; }

1. 贴上报错信息
   以上方法为什么实现不了。。。求真相。。

2. 贴上相关截图

3. 已经尝试过哪些方法仍然没解决（附上相关链接）